Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.1.6.6
REX640
Technical Manual
time is still counting, the reset timer is activated. If the drop-off time exceeds the set
Reset delay time, the operating timer is reset.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is available
in the monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting Configuration/System/
Blocking mode which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK signal activation is
preselected with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode,
the operation timer is frozen to the prevailing value. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the OPERATE output is not activated.

Application

The motor protection during stall is primarily needed to protect the motor from
excessive temperature rise, as the motor draws large currents during the stall phase.
This condition causes a temperature rise in the stator windings. Due to reduced speed,
the temperature also rises in the rotor. The rotor temperature rise is more critical when
the motor stops.
The physical and dielectric insulations of the system deteriorate with age and the
deterioration is accelerated by the temperature increase. Insulation life is related to the
time interval during which the insulation is maintained at a given temperature.
An induction motor stalls when the load torque value exceeds the breakdown torque
value, causing the speed to decrease to zero or to some stable operating point well
below the rated speed. This occurs, for example, when the applied shaft load is
suddenly increased and is greater than the producing motor torque due to the bearing
failures. This condition develops a motor current almost equal to the value of the
locked-rotor current.
JAMPTOC is designed to protect the motor in stall or mechanical jam situations
during the running state. To provide a good and reliable protection for motors in a stall
situation, the temperature effects on the motor have to be kept within the allowed
limits.
Section 4
Protection functions
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